Method for stitching multiple converging paths

ABSTRACT

A method of stitching converging path segments to aesthetically label Y-intersections, path bifurcations or splits in roads or the like entails determining which pair of adjacent path segments subtend the largest angle. The path segments subtending the largest angle are reconstructed (stitched together) and a single instance of the label is then rendered along the reconstructed path. Although this stitching can be performed on the client device, pre-stitching server-side is even more efficient in terms of economizing over-the-air bandwidth and onboard processing resources.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional PatentApplication No. 60/788,434 entitled “Methods and Apparatus forDynamically Labelling Map Objects in Visually Displayed Maps of MobileCommunication Devices” filed on Mar. 31, 2006 and from U.S. ProvisionalPatent Application No. 60/787,541 entitled “Method and System forDistribution of Map Content to Mobile Communication Devices” filed onMar. 31, 2006.

TECHNICAL FIELD

The present disclosure relates generally to wireless communicationsdevices and, in particular, to techniques for generating map content onwireless communications devices.

BACKGROUND

Wireless communications devices such as the BlackBerry® by Research inMotion Limited enable users to download map content from web-based datasources such as BlackBerry Maps™, Google Maps™ or Mapquest™. Downloadedmap content is displayed on a small LCD display screen of the wirelesscommunications device for viewing by the user. The user can pan up anddown and side to side as well as zoom in or out. Due to the smalldisplay on the device and due to the limited over-the-air (OTA)bandwidth, there is a need to optimize the delivery and handling of themap data.

With the increasing availability of wireless communications deviceshaving onboard Global Positioning System (GPS) receivers for providinglocation-based services (LBS), the efficient delivery and handling ofmap data is increasingly important.

In some systems, map data, including label data for labelling mapfeatures, is communicated from map servers to wireless communicationsdevices in discrete portions which are assembled client-side to providethe map content requested by the user. Typically, portions forming apath or other feature are stitched together prior to rendering so as tofacilitate labelling. However, when reconstructing, for example, a pathfrom discrete portions of data, however, redundant labelling can occurif labels associated with each portion of data are rendered for the samefeature. Thus, the issue of label redundancy should be addressed eitherclient-side and/or server-side. However, due to the limited over-the-airbandwidth and the limited onboard processing resources of most wirelessdevices, it is preferable to run computationally intensive algorithmsserver side in order to reduce the data traffic to the device as well asthe onboard processing requirements.

In terms of labelling, a specific problem arises when labelling aY-intersection where a single path splits into two branches, such aswhen a two-lane highway bifurcates into a divided four-lane highway.Each of the three path segments forming the Y-intersection could haveits own label associated therewith. A current stitching techniquecompiles a list of all path segments with respective labels, searchesthe list of segments for identical labels and common endpoints, and then“blindly” stitches the first two segments it finds that have the samelabel and a common endpoint without determining whether the listcontains any other segments having the same label and a common endpoint.If the two of the three paths are stitched based on this technique, thelabel may end up wrapping around onto itself if the application stitchestogether the two branches of the Y-intersection. When the label foldsback onto itself, as illustrated in FIG. 6, the result is clearlyunsatisfactory in terms of readability.

Accordingly, a technique to efficiently and aesthetically labelY-intersections (or any other map features where at least three pathsegments converge) remains highly desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present technology will becomeapparent from the following detailed description, taken in combinationwith the appended drawings, in which:

FIG. 1 is a block diagram schematically illustrating pertinentcomponents of a wireless communications device and of a wirelesscommunications network for implementing the present technology;

FIG. 2 is a more detailed block diagram of a wireless communicationsdevice on which the present technology can be implemented;

FIG. 3A is a system diagram of exemplary network components whichprovide mapping functionality in the wireless communications devices ofFIG. 1 and FIG. 2;

FIG. 3B illustrates, by way of example, a message exchange between awireless communications device and a map server for downloading mapcontent to the wireless communications device based on the system ofFIG. 3A;

FIG. 3C is a diagram showing a preferred Maplet data structure;

FIG. 4 is a schematic depiction of another example of a wireless networkhaving an applications gateway for optimizing the downloading of mapdata from map servers to wireless communications devices on which thepresent technology can be implemented;

FIG. 5A is a flowchart presenting steps of a method of displaying a mapon a wireless device by stitching together on the client side the twopath segments subtending the largest angle in a Y-intersection togenerate a reconstructed path along which a single label is rendered;

FIG. 5B is a flowchart presenting steps of a method of displaying a mapon a wireless device by pre-stitching on the server side the two pathsegments subtending the largest angle in a Y-intersection to generate areconstructed path along which a single label is rendered;

FIG. 6 schematically depicts the potential difficulties of labelling aY-intersection that may be encountered when path segments of aY-intersection are randomly stitched;

FIG. 7 schematically depicts a method of aesthetically labelling aY-intersection by stitching together the pair of adjacent path segmentssubtending the largest angle;

FIG. 8 schematically depicts an angle determination based on vector pathsegments for the segments forming the Y-intersection;

FIG. 9 schematically depicts another example involving labelling of acul-de-sac having three path segments;

FIG. 10 shows the vector angle determination for the example of FIG. 9;

FIG. 11 schematically depicts yet another example involving labelling ofa waterway having three path segments; and

FIG. 12 shows the vector angle determination for the example of FIG. 11.

It will be noted that throughout the appended drawings, like featuresare identified by like reference numerals.

DETAILED DESCRIPTION

The present technology provides, in general, a method of stitchingmultiple converging paths of a map to be displayed on a wirelesscommunications device. Map data, including label data, is downloadedover-the-air in small, discrete portions or sets of data, each with itsown label data for labelling features of the map. Because the data isdownloaded in discrete portions, segments of a common path may requirestitching together either server-side and/or client-side in order toavoid redundant labelling.

This technology addresses the specific labelling problem that arises atintersections where at least three path segments from discretelydownloaded data sets come together. To aesthetically label, for example,a Y-intersection, the server and/or wireless device must first identifyY-intersections or splits/bifurcations where one path divides into two(or conversely where two paths merge into one). For example, aY-intersection can be found where a two-lane highway splits into afour-lane divided highway (or conversely when the four-lane dividedhighway merges into a two-lane highway). As another example, aY-intersection can be found where a boulevard splits around a median(or, conversely, merges where the median ends).

After the three path segments constituting the Y-intersection areidentified, the angle subtending each pair of adjacent path segments isdetermined. The pair of path segments subtending the largest angle isthen stitched together to form a reconstructed path. The server and/orwireless device then renders a single (preferably centrally-positioned)instance of the label along the reconstructed path. Stitching as manysegments as possible reduces label redundancy, thereby minimizing theamount of label data traffic that needs to be transmitted to the clientdevice. Stitching as many segments as possible also provides long pathsto facilitate placement of labels and avoidance of collisions with otherlabels.

The third (“unstitched”) path segment is not stitched to the other two,i.e. it is not stitched to the reconstructed path. A label is preferablynot rendered along the third, “unstitched” path segment, although inparticular cases it may be advantageous to do so, in order to improveoverall readability of the map, e.g. in a case where it is not readilyapparent given the label positions that the third, “unstitched” pathsegment is part of the same path.

Thus, an aspect of the present technology is a method of stitchingmultiple converging paths of a map to be displayed on a wirelesscommunications device. The method includes steps of providing map datafor rendering the map on a display of the device, the map data includinglabel data for labelling paths on the map. Once the data is provided,the next step entails identifying at least three path segments thatconverge to a common point on the map, each of the path segments havingan identical label. After the three or more path segments areidentified, the next step involves determining an angle subtended byeach pair of adjacent path segments in order to identify which pair ofadjacent path segments subtends the largest angle. Once the pair ofadjacent path segments subtending the largest angle is determined, thenext steps entail generating a reconstructed path by stitching togetherthe pair of adjacent path segments subtending the largest angle andrendering a single instance of the label along the reconstructed path.This method of stitching multiple converging paths of a map ispreferably performed server-side, where “pre-stitching” computations canbe handled most easily and to furthermore avoid having to transmitredundant labels to the device. This method, however, can also beperformed client-side, i.e. on the client device.

Another aspect of the present technology is a computer program productthat includes a computer-readable medium having code executable by aprocessor to perform the steps of the foregoing method when the computerprogram product is loaded into memory and executed on the processor. Thecomputer program product can be loaded into a memory of a server forperforming server-side “pre-stitching” and/or into a memory of awireless communications device for performing client-side stitching.

Yet another aspect of the present technology is a wirelesscommunications device for enabling a user of the device to display a mapon the device. The wireless device has an input device for enabling theuser to cause the device to obtain map data for rendering the map to bedisplayed on a display of the device, the map data including label datafor labelling paths on the map. The wireless device also has a memoryfor storing code to instruct a processor to identify at least three pathsegments that converge to a common point on the map, each of the pathsegments having an identical label, determine an angle subtended by eachpair of adjacent path segments in order to identify which pair ofadjacent path segments subtends the largest angle, generate areconstructed path by stitching together the pair of adjacent pathsegments subtending the largest angle, and render a single instance ofthe label along the reconstructed path.

The details and particulars of these aspects of the technology will nowbe described below, by way of example, with reference to the attacheddrawings.

FIG. 1 is a block diagram of a communication system 100 which includes awireless communications device 102 (also referred to as a mobilecommunications device) which communications through a wirelesscommunication network 104. For the purposes of the presentspecification, the expression “wireless communications device”encompasses not only a wireless handheld, cell phone or wireless-enabledlaptop but also any mobile communications device or portablecommunications device such as a satellite phone, wireless-enabled PDA orwireless-enabled MP3 player. In other words, for the purposes of thisspecification, “wireless” shall be understood as encompassing not onlystandard cellular or microwave RF technologies, but also any othercommunications technique that conveys data over the air using anelectromagnetic signal.

The wireless communications device 102 preferably includes a visualdisplay 112, e.g. an LCD screen, a keyboard 114 (or keypad), andoptionally one or more auxiliary user interfaces (UI) 116, each of whichis coupled to a controller 106. The controller 106 is also coupled toradio frequency (RF) transceiver circuitry 108 and an antenna 110.Typically, controller 106 is embodied as a central processing unit (CPU)which runs operating system software in a memory device (described laterwith reference to FIG. 2). Controller 106 normally controls the overalloperation of the wireless communications device 102, whereas signalprocessing operations associated with communications functions aretypically performed in the RF transceiver circuitry 108. Controller 106interfaces with the display screen 112 to display received information,stored information, user inputs, and the like. Keyboard/keypad 114,which may be a telephone-type keypad or a full QWERTY keyboard, isnormally provided for entering commands and data.

The wireless communications device 102 sends communication signals toand receives communication signals from network 104 over a wireless linkvia antenna 110. RF transceiver circuitry 108 performs functions similarto those of station 118 and Base Station Controller (BSC) 120,including, for example, modulation and demodulation, encoding anddecoding, and encryption and decryption. It will be apparent to thoseskilled in the art that the RF transceiver circuitry 108 will be adaptedto the particular wireless network or networks in which the wirelesscommunications device is intended to operate.

The wireless communications device 102 includes a battery interface 134for receiving one or more rechargeable batteries 132. Battery 132provides electrical power to electrical circuitry in the device 102, andbattery interface 134 provides for a mechanical and electricalconnection for battery 132. Battery interface 134 is couple to aregulator 136 which regulates power to the device. When the wirelessdevice 102 is fully operationally, an RF transmitter of RF transceivercircuitry 108 is typically keyed or turned on only when it is sending tonetwork, and is otherwise turned off to conserve resources. Similarly,an RF receiver of RF transceiver circuitry 108 is typically periodicallyturned off to conserve power until it is needed to receive signals orinformation (if at all) during designated time periods.

Wireless communications device 102 operates using a Subscriber IdentityModule (SIM) 140 which is connected to or inserted in the wirelesscommunications device 102 at a SIM interface 142. SIM 140 is one type ofa conventional “smart card” used to identify an end user (or subscriber)of wireless device 102 and to personalize the device, among otherthings. By inserting the SIM card 140 into the wireless communicationsdevice 102, an end user can have access to any and all of his subscribedservices. SIM 140 generally includes a processor and memory for storinginformation. Since SIM 140 is coupled to SIM interface 142, it iscoupled to controller 106 through communication lines 144. In order toidentify the subscriber, SIM 140 contains some user parameters such asan International Mobile Subscriber Identity (IMSI). An advantage ofusing SIM 140 is that end users are not necessarily bound by any singlephysical wireless device. SIM 140 may store additional user informationfor the wireless device as well, including datebook (calendar)information and recent call information.

The wireless communications device 102 may consist of a single unit,such as a data communication device, a cellular telephone, a GlobalPositioning System (GPS) unit, a multiple-function communication devicewith data and voice communication capabilities, a wireless-enabledpersonal digital assistant (PDA), or a wireless-enabled laptop computer.Alternatively, the wireless communications device 102 may be amultiple-module unit comprising a plurality of separate components,including but in no way limited to a computer or other device connectedto a wireless modem. In particular, for example, in the block diagram ofFIG. 1, RF circuitry 108 and antenna 110 may be implemented as a radiomodem unit that may be inserted into a port on a laptop computer. Inthis case, the laptop computer would include display 112, keyboard 114,one or more auxiliary UIs 116, and controller 106 embodied as thecomputer's CPU.

The wireless communications device 102 communicates in and through awireless communication network 104. The wireless communication networkmay be a cellular telecommunications network. In the example presentedin FIG. 1, wireless network 104 is configured in accordance with GlobalSystems for Mobile communications (GSM) and General Packet Radio Service(GPRS) technologies. Although wireless communication network 104 isdescribed herein as a GSM/GPRS-type network, any suitable networktechnologies may be utilized such as Code Division Multiple Access(CDMA), Wideband CDMA (WCDMA), whether 2G, 3G, or Universal MobileTelecommunication System (UMTS) based technologies. In this example, theGSM/GPRS wireless network 104 includes a base station controller (BSC)120 with an associated tower station 118, a Mobile Switching Center(MSC) 122, a Home Location Register (HLR) 132, a Serving General PacketRadio Service (GPRS) Support Node (SGSN) 126, and a Gateway GPRS SupportNode (GGSN) 128. MSC 122 is coupled to BSC 120 and to a landlinenetwork, such as a Public Switched Telephone Network (PSTN) 124. SGSN126 is coupled to BSC 120 and to GGSN 128, which is, in turn, coupled toa public or private data network 130 (such as the Internet). HLR 132 iscoupled to MSC 122, SGSN 126 and GGSN 128.

Tower station 118 is a fixed transceiver station. Tower station 118 andBSC 120 may be referred to as transceiver equipment. The transceiverequipment provides wireless network coverage for a particular coveragearea commonly referred to as a “cell”. The transceiver equipmenttransmits communication signals to and receives communication signalsfrom wireless communications devices 102 within its cell via station118. The transceiver equipment normally performs such functions asmodulation and possibly encoding and/or encryption of signals to betransmitted to the wireless communications device in accordance withparticular, usually predetermined, communication protocols andparameters. The transceiver equipment similar demodulates and possiblydecodes and decrypts, if necessary, any communication signals receivedfrom the wireless communications device 102 transmitting within itscell. Communication protocols and parameters may vary between differentnetworks. For example, one network may employ a different modulationscheme and operate at different frequencies than other networks.

The wireless link shown in communication system 100 of FIG. 1 representsone or more different channels, typically different radio frequency (RF)channels, and associated protocols used between wireless network 104 andwireless communications device 102. An RF channel is a limited resourcethat must be conserved, typically due limits in overall bandwidth and alimited battery power of the wireless device 102. Those skilled in theart will appreciate that a wireless network in actual practice mayinclude hundreds of cells, each served by a station 118, depending upondesired overall expanse of network coverage. All pertinent componentsmay be connected by multiple switches and routers (not shown),controlled by multiple network controllers.

For all wireless communications devices 102 registered with a networkoperator, permanent data (such as the user profile associated with eachdevice) as well as temporary data (such as the current location of thedevice) are stored in the HLR 132. In case of a voice call to thewireless device 102, the HLR 132 is queried to determine the currentlocation of the device 102. A Visitor Location Register (VLR) of MSC 122is responsible for a group of location areas and stores the data ofthose wireless devices that are currently in its area of responsibility.This includes parts of the permanent data that have been transmittedfrom HLR 132 to the VLR for faster access. However, the VLR of MSC 122may also assign and store local data, such as temporary identifications.Optionally, the VLR of MSC 122 can be enhanced for more efficientco-ordination of GPRS and non-GPRS services and functionality (e.g.paging for circuit-switched calls which can be performed moreefficiently via SGSN 126, and combined GPRS and non-GPRS locationupdates).

Serving GPRS Support Node (SGSN) 126 is at the same hierarchical levelas MSC 122 and keeps track of the individual locations of wirelessdevices 102. SGSN 126 also performs security functions and accesscontrol. Gateway GPRS Support Node (GGSN) 128 provides internetworkingwith external packet-switched networks and is connected with SGSNs (suchas SGSN 126) via an IP-based GPRS backbone network. SGSN 126 performsauthentication and cipher setting procedures based on the samealgorithms, keys, and criteria as in existing GSM. In conventionaloperation, cell selection may be performed autonomously by wirelessdevice 102 or by the transceiver equipment instructing the wirelessdevice to select a particular cell. The wireless device 102 informswireless network 104 when it reselects another cell or group of cells,known as a routing area.

In order to access GPRS services, the wireless device 102 first makesits presence known to wireless network 104 by performing what is knownas a GPRS “attach”. This operation establishes a logical link betweenthe wireless device 102 and SGSN 126 and makes the wireless device 102available to receive, for example, pages via SGSN, notifications ofincoming GPRS data, or SMS messages over GPRS. In order to send andreceive GPRS data, the wireless device 102 assists in activating thepacket data address that it wants to use. This operation makes thewireless device 102 known to GGSN 128; internetworking with externaldata networks can thereafter commence. User data may be transferredtransparently between the wireless device 102 and the external datanetworks using, for example, encapsulation and tunneling. Data packetsare equipped with GPRS-specific protocol information and transferredbetween wireless device 102 and GGSN 128.

Those skilled in the art will appreciate that a wireless network may beconnected to other systems, possibly including other networks, notexplicitly shown in FIG. 1. A network will normally be transmitting atvery least some sort of paging and system information on an ongoingbasis, even if there is no actual packet data exchanged. Although thenetwork consists of many parts, these parts all work together to resultin certain behaviours at the wireless link.

FIG. 2 is a detailed block diagram of a preferred wirelesscommunications device 202. The wireless device 202 is preferably atwo-way communication device having at least voice and advanced datacommunication capabilities, including the capability to communicate withother computer systems. Depending on the functionality provided by thewireless device 202, it may be referred to as a data messaging device, atwo-way pager, a cellular telephone with data message capabilities, awireless Internet appliance, or a data communications device (with orwithout telephony capabilities). The wireless device 202 may communicatewith any one of a plurality of fixed transceiver stations 200 within itsgeographic coverage area.

The wireless communications device 202 will normally incorporate acommunication subsystem 211, which includes a receiver 212, atransmitter 214, and associated components, such as one or more(preferably embedded or internal) antenna elements 216 and 218, localoscillators (LO's) 213, and a processing module such as a digital signalprocessor (DSP) 220. Communication subsystem 211 is analogous to RFtransceiver circuitry 108 and antenna 110 shown in FIG. 1. As will beapparent to those skilled in the field of communications, the particulardesign of communication subsystem 211 depends on the communicationnetwork in which the wireless device 202 is intended to operate.

The wireless device 202 may send and receive communication signals overthe network after required network registration or activation procedureshave been completed. Signals received by antenna 216 through the networkare input to receiver 212, which may perform common receiver functionsas signal amplification, frequency down conversion, filtering, channelselection, and the like, and, as shown in the example of FIG. 2,analog-to-digital (A/D) conversion. A/D conversion of a received signalallows more complex communication functions such as demodulation anddecoding to performed in the DSP 220. In a similar manner, signals to betransmitted are processed, including modulation and encoding, forexample, by DSP 220. These DSP-processed signals are input totransmitter 214 for digital-to-analog (D/A) conversion, frequency upconversion, filtering, amplification and transmission over communicationnetwork via antenna 218. DSP 220 not only processes communicationsignals, but also provides for receiver and transmitter control. Forexample, the gains applied to communication signals in receiver 212 andtransmitter 214 may be adaptively controlled through automatic gaincontrol algorithms implemented in the DSP 220.

Network access is associated with a subscriber or user of the wirelessdevice 202, and therefore the wireless device requires a SubscriberIdentity Module or SIM card 262 to be inserted in a SIM interface 264 inorder to operate in the network. SIM 262 includes those featuresdescribed in relation to FIG. 1. Wireless device 202 is abattery-powered device so it also includes a battery interface 254 forreceiving one or more rechargeable batteries 256. Such a battery 256provides electrical power to most if not all electrical circuitry in thedevice 102, and battery interface provides for a mechanical andelectrical connection for it. The battery interface 254 is coupled to aregulator (not shown) which provides a regulated voltage V to all of thecircuitry.

Wireless communications device 202 includes a microprocessor 238 (whichis one implementation of controller 106 of FIG. 1) which controlsoverall operation of wireless device 202. Communication functions,including at least data and voice communications, are performed throughcommunication subsystem 211. Microprocessor 238 also interacts withadditional device subsystems such as a display 222, a flash memory 224,a random access memory (RAM) 226, auxiliary input/output (I/O)subsystems 228, a serial port 230, a keyboard 232, a speaker 234, amicrophone 236, a short-range communications subsystem 240, and anyother device subsystems generally designated at 242. Some of thesubsystems shown in FIG. 2 perform communication-related functions,whereas other subsystems may provide “resident” or on-board functions.Notably, some subsystems, such as keyboard 232 and display 222, forexample, may be used for both communication-related functions, such asentering a text message for transmission over a communication network,and device-resident functions such as a calculator or task list.Operating system software used by the microprocessor 238 is preferablystored in a persistent (non-volatile) store such as flash memory 224,which may alternatively be a read-only memory (ROM) or similar storageelement (not shown). Those skilled in the art will appreciate that theoperating system, specific device applications, or parts thereof, may betemporarily loaded into a volatile store such as RAM 226.

Microprocessor 238, in addition to its operating system functions,enables execution of software applications on the wireless device 202. Apredetermined set of applications which control basic device operations,including at least data and voice communication applications, willnormally be installed on the device 202 during its manufacture. Forexample, the device may be pre-loaded with a personal informationmanager (PIM) having the ability to organize and manage data itemsrelating to the user's profile, such as e-mail, calendar events, voicemails, appointments, and task items. Naturally, one or more memorystores are available on the device 202 and SIM, 256 to facilitatestorage of PIM data items and other information.

The PIM application preferably has the ability to send and receive dataitems via the wireless network. PIM data items may be seamlesslyintegrated, synchronized, and updated via the wireless network, with thewireless device user's corresponding data items stored and/or associatedwith a host computer system thereby creating a mirrored host computer onthe wireless device 202 with respect to such items. This is especiallyadvantageous where the host computer system is the wireless deviceuser's office computer system. Additional applications may also beloaded into the memory store(s) of the wireless communications device202 through the wireless network, the auxiliary I/O subsystem 228, theserial port 230, short-range communications subsystem 240, or any othersuitable subsystem 242, and installed by a user in RAM 226 or preferablya non-volatile store (not shown) for execution by the microprocessor238. Such flexibility in application installation increases thefunctionality of the wireless device 202 and may provide enhancedonboard functions, communication-related functions or both. For example,secure communication applications may enable electronic commercefunctions and other such financial transactions to be performed usingthe wireless device 202.

In a data communication mode, a received signal such as a text message,an e-mail message, or a web page download will be processed bycommunication subsystem 211 and input to microprocessor 238.Microprocessor 238 will preferably further process the signal for outputto display 222 or alternatively to auxiliary I/O device 228. A user ofthe wireless device 202 may also compose data items, such as emailmessages, for example, using keyboard 232 in conjunction with display222 and possibly auxiliary I/O device 228. Keyboard 232 is preferably acomplete alphanumeric keyboard and/or telephone-type keypad. Thesecomposed items may be transmitted over a communication network throughcommunication subsystem 211.

For voice communications, the overall operation of the wirelesscommunications device 202 is substantially similar, except that thereceived signals would be output to speaker 234 and signals fortransmission would be generated by microphone 236. Alternative voice oraudio I/O subsystems, such as a voice message recording subsystem, mayalso be implemented on the wireless device 202. Although voice or audiosignal output is preferably accomplished primarily through speaker 234,display 222 may also be used to provide an indication of the identity ofthe calling party, duration on a voice call, or other voice call relatedinformation, as some examples.

Serial port 230 in FIG. 2 is normally implemented in a personal digitalassistant (PDA)-type communication device for which synchronization witha user's desktop computer is a desirable, albeit optional, component.Serial port 230 enables a user to set preferences through an externaldevice or software application and extends the capabilities of wirelessdevice 202 by providing for information or software downloads to thewireless device 202 other than through the wireless network. Thealternate download path may, for example, be used to load an encryptionkey onto the wireless device 202 through a direct and thus reliable andtrusted connection to thereby provide secure device communications.

Short-range communications subsystem 240 of FIG. 2 is an additionaloptional component which provides for communication between mobilestation 202 and different systems or devices, which need not necessarilybe similar devices. For example, subsystem 240 may include an infrareddevice and associated circuits and components, or a Bluetooth™communication module to provide for communication with similarly-enabledsystems and devices. Bluetooth™ is a trademark of Bluetooth SIG, Inc.

FIG. 3A is a system diagram of network components which provide mappingfunctionality in the wireless communication devices of FIGS. 1 and 2. Toachieve this, a mapping application is also provided in memory of thewireless communications device for rendering visual maps in its display.Wireless communications devices 202 are connected over a mobile carriernetwork 303 for communication through a firewall 305 to a relay 307. Arequest for map data from any one of the wireless communications devices202 is received at relay 307 and passed via a secure channel 309 throughfirewall 311 to a corporate enterprise server 313 and corporate mobiledata system (MDS) server 315. The request is then passed via firewall317 to a public map server and/or to a public location-based service(LBS) server 321 which provides location-based services (LBS) to handlethe request. The network may include a plurality of such map serversand/or LBS servers where requests are distributed and processed througha load distributing server. The map/LBS data may be stored on thisnetwork server 321 in a network database 322, or may be stored on aseparate map server and/or LBS server (not shown). Private corporatedata stored on corporate map/LBS server 325 may be added to the publicdata via corporate MDS server 315 on the secure return path to thewireless device 202. Alternatively, where no corporate servers areprovided, the request from the wireless device 202 may be passed viarelay 307 to a public MDS server 327, which sends the request to thepublic map/LBS server 321 providing map data or other local-basedservice in response to the request. For greater clarity, it should beunderstood that the wireless devices can obtain map data from a “pure”map server offering no location-based services, from an LBS serveroffering location-based services in addition to map content, or from acombination of servers offering map content and LBS.

A Maplet data structure is provided that contains all of the graphic andlabelled content associated with a geographic area (e.g. map featuressuch as restaurants (point features), streets (line features) or lakes(polygon features)). Maplets are structured in Layers of Data Entries(“DEntries”) identified by a “Layer ID” to enable data from differentsources to be deployed to the device and meshed for proper rendering.Each DEntry is representative of one or more artifact or label (or acombination of both) and includes coordinate information (also referredto as a “bounding box” or “bounding area”) to identify the area coveredby the DEntry and a plurality of data points that together represent theartifact, feature or label. For example, a DEntry may be used torepresent a street on a city map (or a plurality of streets), whereinthe various points within the DEntry are separated into different partsrepresenting various portions of the artifact or map feature (e.g.portions of the street). A wireless device may issue a request for themap server to download only those DEntries that are included within aspecified area or bounding box representing an area of interest that canbe represented by, for example, a pair of bottom left, top rightcoordinates.

As depicted in FIG. 3B, the wireless communications device issues one ormore AOI (Area of Interest) requests, DEntry or data requests and MapletIndex requests to the map server for selective downloading of map databased on user context. Thus, rather than transmitting the entire mapdata for an area in reply to each request from the device (which burdensthe wireless link), local caching may be used in conjunction withcontext filtering of map data on the server. For example, if a user'swireless device is GPS enabled and the user is traveling in anautomobile at 120 km/h along a freeway then context filtering can byemployed to prevent downloading of map data relating to passing sidestreets. Or, if the user is traveling in an airplane at 30,000 feet,then context filtering can be employed to prevent downloading of mapdata for any streets whatsoever. Also, a user's context can be defined,for example, in terms of occupation, e.g. a user whose occupation is atransport truck driver can employ context filtering to preventdownloading of map data for side streets on which the user's truck isincapable of traveling, or a user whose occupation is to replenishsupplied of soft drink dispensing machines can employ context filteringto download public map data showing the user's geographical area ofresponsibility with irrelevant features such as lakes and parks filteredout and private map data containing the location of soft drinkdispensing machines superimposed on the public map data.

The Maplet Index request results in a Maplet Index (i.e. only a portionof the Maplet that provides a table of contents of the map dataavailable within the Maplet rather than the entire Maplet) beingdownloaded from the map server to the device, thereby conserving OTA(Over-the-Air) bandwidth and device memory caching requirements. TheMaplet Index conforms to the same data structure as a Maplet, but omitsthe data points. Consequently, the Maplet Index is small (e.g. 300-400bytes) relative to the size of a fully populated Maplet or aconventional bit map, and includes DEntry bounding boxes and attributes(size, complexity, etc.) for all artifacts within the Maplet. As thefield of view changes (e.g. for a location-aware device that displays amap while moving), the device (client) software assesses whether or notit needs to download additional data from the server. Thus, if the sizeattribute or complexity attribute of an artifact that has started tomove into the field of view of the device (but is not yet beingdisplayed) is not relevant to the viewer's current context, then thedevice can choose not to display that portion of the artifact. On theother hand, if the portion of the artifact is appropriate for display,then the device accesses its cache to determine whether the DEntriesassociated with that portion of the artifact have already beendownloaded, in which case the cached content is displayed. Otherwise,the device issues a request for the map server to download all the ofthe DEntries associated with the artifact portion.

By organizing the Maplet data structure in Layers, it is possible toseamlessly combine and display information obtained from public andprivate databases. For example, it is possible for the device to displayan office building at a certain address on a street (e.g. a 1^(st)z-order attribute from public database), adjacent a river (e.g. a 2^(nd)z-order attribute from public database), with a superimposed floor planeof the building to show individual offices (e.g. 11^(th) z-orderattribute from a private database, accessible through a firewall).

Referring back to FIG. 3A, within the network having map server(s)and/or LBS server(s) 321 and database(s) 322 accessible to it, all ofthe map data for the entire world is divided and stored as a gridaccording to various levels of resolution (zoom), as set forth below inTable A. Thus, a single A-level Maplet represents a 0.05×0.05 degreegrid area; a single B-level Maplet represents a 0.5×0.5 degree gridarea; a single C-level Maplet represents a 5×5 degree grid area; asingle D-level Maplet represents a 50×50 degree grid area; and a singleE level Maplet represents the entire world in a single Maplet. It isunderstood that Table A is only an example of a particular Maplet griddivision; different grid divisions having finer or coarser granularitymay, of courser, be substituted. A Maplet includes a set of layers, witheach layer containing a set of DEntries, and each DEntry containing aset of data points.

TABLE A # of Maplets # of Maplets # of Maplets Grid to cover to cover tocover Level (degrees) the World North America Europe A 0.05 × 0.0525,920,000 356,000 100,000 B 0.5 × 0.5 259,200 6,500 1000 C 5 × 5 2,59296 10 D 50 × 50 32 5 5 E World 1 1 1

As mentioned above, three specific types of requests may be generated bya wireless communications device (i.e. the client)—AOI requests, DEntryrequests and Maplet Index requests. The requests may be generatedseparately or in various combinations, as discussed in greater detailbelow. An AOI (area of interest) request calls for all DEntries in agiven area (bounding box) for a predetermined or selected set of z-orderLayers. The AOI request is usually generated when the device moves to anew area so as to fetch DEntries for display before the device clientknows what is available in the Maplet. The Maplet Index has the exactsame structure as a Maplet but does not contain complete DEntries (i.e.the data Points actually representing artifacts and labels are omitted).Thus, a Maplet Index defines what Layers and DEntries are available fora given Maplet. A data or DEntry request is a mechanism to bundletogether all of the required Dentries for a given Maplet.

Typically, AOI and Maplet Index requests are paired together in the samemessage, although they need not be, while DEntry requests are generatedmost often. For example, when a wireless device moves into an area forwhich no information has been stored on the device client, the MapletIndex request returns a Maplet Index that indicates what data the clientcan specifically request from the server 321, while the AOI requestreturns any DEntries within the area of interest for the specifiedLayers (if they exist). In the example requests shown on FIG. 3B, thedesired Maplet is identified within a DEntry request by specifying thebottom-left Maplet coordinate. In addition, the DEntry request mayinclude a layer mask so that unwanted Layers are not downloaded, aDEntry mask so that unwanted data Points are not downloaded, and zoomvalues to specify a zoom level for the requested DEntry. Once the deviceclient has received the requested Maplet Index, the client typicallythen issues multiple DEntry requests to ask for specific DEntries (sincethe client knows all of the specific DEntries that are available basedon the Maplet Index).

In this particular implementation, a collection of 20×20 A-level Maplets(representing a 1×1 degree square) is compiled into a Maplet Block File(.mbl). An .mbl file contains a header which specifies the offset andlength of each Maplet in the .mbl file. The same 20×20 collection ofMaplet index data is compiled into a Maplet Index file (.mbx). The .mbland .mbx file structures are set forth in Tables B and C, respectively.

TABLE B Address Offset Offset Length 0x000 Maplet #0 Offset Maplet #0Length (4 bytes) (4 bytes) 0x008 Maplet #1 Offset Maplet #1 Length 0x010Maplet #2 Offset Maplet #2 Length . . . . . . . . . 0xC78 Maplet #399Maplet #399 Offset Length 0xC80 Beginning of Maplet #0 0xC80 + Size ofMaplet #0 Beginning of Maplet #1 0xC80 + Size of Maplet #0 + #1Beginning of Maplet #2 . . . . . . 0xC80 + Σ of Size of Beginning ofMaplet #399 Maplets (#0:#398)

In Table B, the offset of Maplet #0 is 0x0000_(—)0000 since, in thisparticular example, the data structure is based on the assumption thatthe base address for the actual Maplet data is 0x0000_(—)0C80. Thereforethe absolute address for Maplet #0 data is: Maplet #0 Address=BaseAddress (0x0000_(—)0C80)+Maplet #0 Offset (0x0000_(—)0000), andadditional Maplet addresses are calculated as: Maplet #(n+1)Offset=Maplet #(n) Offset+Maplet #(n) Length. If a Maplet has no data ordoes not exist, the length parameter is set to zero (0x0000_(—)0000).

TABLE C Address Offset Offset (4 bytes) Length (4 bytes) 0x000 MapletIndex #0 Maplet Index #0 Offset Length 0x008 Maplet Index #1 MapletIndex #1 Offset Length 0x010 Maplet Index #2 Maplet Index #2 OffsetLength . . . . . . . . . 0xC78 Maplet Index #399 Maplet Index #399Offset Length 0xC80 Beginning of Maplet Index #0 0xC80 + Size ofBeginning of Maplet Index #1 Maplet Index #0 0xC80 + Size of Beginningof Maplet Index #2 Maplet Index #0 + #1 . . . . . . 0xC80 + Σ ofBeginning of Maplet Index #399 Size of Maplet Indices (#0:#399)

In Table C, the offset of Maplet Index #0 is 0x0000_(—)0000 since,according to an exemplary embodiment the data structure is based on theassumption that the base address for the actual Maplet index data is0x0000_(—)0C80. Therefore, the absolute address for Maplet Index #0 datais: Maplet Index #0 Address=Base Address (0x0000_(—)0C80)+Maplet Index#0 Offset (0x0000_(—)0000), and additional Maplet index addresses arecalculated as: Maplet Index #(n+1) Offset=Maplet Index #(n)Offset+Maplet Index #(n) Length. If a Maplet Index has no data or doesnot exist, the length parameter is set to zero (0x0000_(—)0000).

FIG. 3C and Table D (below), in combination, illustrate, by way ofexample only, a basic Maplet data structure. Generally, as noted above,the Maplet data structure can be said to include a Maplet Index (i.e. anindex of the DEntries, each of which is representative of either anartifact or a label or both) together with data Points for each DEntrythat actually form such artifacts and labels. In this example, eachMaplet includes a Map ID (e.g. 0xA1B1C1D1), the # of Layers in theMaplet, and a Layer Entry for each Layer. The Map ID identifies the dataas a valid Maplet, and according to one alternative, may also be used toidentify a version number for the data. The # of Layers is an integerwhich indicates the number of Layers (and therefore Layer Entries) inthe Maplet. Each Layer Entry defines rendering attributes and isfollowed by a list of DEntries for each Layer. The above forms a MapletIndex. For a complete Maplet, each DEntry contains a set of data Points(referred to herein as oPoints) or Labels). It will be noted that Layerscan have multiple DEntries and the complete list of DEntries and Pointsare grouped by Layer and separated by a Layer Separator (e.g. hex value0xEEEEEEEE). In this example, each Layer Entry is 20 bytes long, and aDEntry is 12 bytes long. However, the number of Layers, number ofDEntries per Layer and the number of Points per DEntry depends on themap data and is generally variable.

Table D provides a high “byte-level” description of a Maplet for thisexample.

TABLE D Data Quantity Total # of Bytes Map ID 1 4 bytes # of Layers 1 4bytes Layer Entries # of 20 bytes x (# of Layers) Layers DEntry of a x(# of # of 12 bytes x (Σ of the # Layer DEntries Layers of DEntries ineach in a Layer)+ Points for Layer) 4 bytes x (Σ of the # of DEntry of aPoints in each DEntry in Layer each Layer)+ Layer Separator 4 bytes x (#of Layers)

By way of a further example, the wireless network 200 depicted in FIG. 4can include an applications gateway (AG) 350 for optimizing data flowfor onboard applications such as a mapping application 500 stored inmemory (e.g. stored in a flash memory 224) and executable by themicroprocessor 238 of the wireless device 202.

As shown in FIG. 4, the wireless network 200 hosts a plurality ofhandheld wireless communications devices 202 (such as the BlackBerry® byResearch in Motion Limited) having voice and data capabilities (for bothe-mail and web browsing) as well as a full QWERTY keyboard. Thesewireless communications devices 202 can access Web-based map data onpublic map servers 400 hosted on the Internet or other data network 130via the applications gateway (AG) 350 which mediates and optimizes dataflow between the wireless network 200 and the data network by performingvarious mappings, compressions and optimizations on the data.

The map server extracts generic map content from a GeographicalInformation Systems (GIS) map database (e.g. Navtech®, TelAtlas®, etc.)at a specified level of resolution (zoom level). Custom graphicsassociated with the query, such as highlighted route, pushpin forcurrent position or street address, etc. are post-processed and mergedby the server with the generic map content. Relevant screen graphics arethen labelled, and the merged map graphic is compressed and delivered tothe device for display.

In operation, a user of the wireless communications device 202 uses aninput device such as keyboard 232 and/or thumbwheel/trackball 233 tocause the microprocessor 238 to open the map application 500 stored inthe memory 224. Using the keyboard 232 and thumbwheel/trackball 233, theuser specifies a map location on the map application 500. In response tothis request/command, the microprocessor 238 instructs the RFtransceiver circuitry 211 to transmit the request over the air throughthe wireless network 104. The request is processed by the AG 350 andforwarded into the data network (Internet) using standardpacket-forwarding protocols to one or more of the public and/or privatemap servers 400, 410. Accessing a private map server 410 behind acorporate firewall 420 was described above with reference to FIG. 3A.Map data downloaded from these one or more map servers 400, 410 is thenforwarded in data packets through the data network and mapped/optimizedby the AG 350 for wireless transmission through the wireless network 104to the wireless communications device 202 that originally sent therequest.

The downloaded map data can be cached locally in RAM 226, and displayedon the display 222 or graphical user interface (GUI) of the device afterthe map application 500 reconstructs or “stitches together” portions offeatures or constituent path segments to generate a reconstructed mapfeature or path, in a client-side implementation as will elaboratedbelow, so that a single instance of the label can be centrally renderedfor the reconstructed feature or path (provided it does not collide withanother label of higher priority). Alternatively, server-sidepre-stitching can be performed to eliminate redundant labels, thusalleviating both onboard processing and OTA bandwidth requirements. If afurther request is made by the user (or if the user wants a change inthe field of view by zooming or panning), the device will check whetherthe data required can be obtained from the local cache (RAM 226). Ifnot, the device issues a new request to the one or more map servers 400,410 in the same manner as described above.

As described earlier, map data can optionally be downloaded first as aMaplet Index enabling the user to then choose which DEntries listed inthe Index to download in full. Furthermore, as described earlier, themap application can include user-configurable context filtering thatenables the user to filter out unwanted map features or artifacts by notdownloading specific DEntries corresponding to those unwanted mapfeatures or artifacts.

As a variant, the wireless communications device can optionally includea Global Positioning System (GPS) receiver (“GPS chip”) 550 forproviding location-based services (LBS) to the user in addition to mapcontent. Embedding a GPS chip 550 capable of receiving and processingsignals from GPS satellites enable the GPS chip to generate latitude andlongitude coordinates, thus making the device “location aware”. Toobtain local-based services, the map application within the wirelesscommunications device sends a request to the map server for informationrelating to a city, restaurant, street address, route, etc. If thedevice is “location aware”, the request would include the currentlocation of the device.

In lieu of, or in addition to, GPS coordinates, the location of thedevice can be determined using triangulation of signals from in-rangebase towers, such as used for Wireless E911. Wireless Enhanced 911services enable a cell phone or other wireless device to be locatedgeographically using radiolocation techniques such as (i) angle ofarrival (AOA) which entails locating the caller at the point wheresignals from two towers intersect; (ii) time difference of arrival(TDOA), which uses multilateration like GPS, except that the networksdetermine the time difference and therefore the distance from eachtower; and (iii) location signature, which uses “fingerprinting” tostore and recall patterns (such as multipath) which mobile phone signalsexhibit at different locations in each cell.

Operation of the systems described above will now be described withreference to the method steps depicted in the flowcharts of FIGS. 5A and5B. FIG. 5A depicts a method of stitching paths that is doneclient-side, i.e. on the device whereas FIG. 5B depicts a method of“pre-stitching” performed server side, which economizes over-the-air(OTA) bandwidth and avoids having to perform label angle calculations onthe device. As depicted in FIG. 5A, the first method of displaying a mapon a wireless communications device includes initial steps of openingthe map application on the device (step 600) and specifying an area ofinterest (AOI) using the map application (step 602), e.g. specifying astreet address, coordinates of latitude or longitude, or clicking on alocation on a world map, etc. In response to the specifying of an AOI,map data is then obtained (step 604) for rendering the map to bedisplayed on the wireless communications device. For the purposes ofthis specification, “providing map data” means either providing the datato a server (for “pre-stitching”) or obtaining data at the client deviceby receiving or downloading the map data over the air, i.e. over awireless link, retrieving the map data from a local cache, ordownloading the map data over a wired connection, or any combinationthereof. In other words, as depicted in FIG. 5A, obtaining map dataincludes steps of determining whether the data is already cached locally(step 604). If the data is locally cached, the map data is retrievedfrom the cache (step 606). Otherwise, if not all of the map data iscached, then the map data is downloaded over the air (step 608).

As depicted in FIG. 5A, once the map data is obtained, the deviceidentifies (step 610) at least three path segments that converge to acommon point on the map, wherein each of the path segments has anidentical label. A point where three path segments having the same labelconverge is referred to herein as a “Y-intersection”, i.e. the point ofconvergence where a path splits/divides/bifurcates (or, conversely,where a divided path merges). Identifying a Y-intersection can be doneby compiling a list of segments and their respective labels and thendetermining whether there are three (or potentially more) segmentshaving the same label and sharing a common endpoint. If that is thecase, then a Y-intersection exists and is flagged. As further depictedin FIG. 5A, after identifying a Y-intersection or a point where threepath segments having the same label converge, the method then entails astep 612 of determining an angle subtended by each pair of adjacent pathsegments in order to identify (step 614) which pair of adjacent pathsegments subtends the largest angle. Once this pair of paths having thelargest angle is identified, the method entails a step 616 of generatinga reconstructed path by stitching together the pair of adjacent pathsegments subtending the largest angle, followed by a step 618 ofrendering a single instance of the label along the reconstructed path.

FIG. 5B presents a method of pre-stitching the paths server-side, whichis more efficient that the method of FIG. 5B because it conserves scarceOTA bandwidth and onboard processing capacity. As depicted, an initialstep 620 entails receiving a request from a wireless communicationsdevice for map data. At step 622, map data (e.g. in the form of DEntries from one or more Maplets) is obtained to enable the server topre-stitch the path segments. The server then identifies anyY-intersections having three or more converging path segments (step624), determines angles between each pair of adjacent path segments(step 626), and then identifies the pair of segments subtending thelargest angle (step 628). Once this is done, the server stitches thepath segments to generate a reconstructed path (step 630) and determineslabelling (step 632) for the reconstructed path by, for example,eliminating redundant labels. By eliminating redundant labels at theserver side, less label data has to be transmitted wirelessly to theclient device. Furthermore, by eliminating redundant labels server side,the device does not need to expend valuable processing capacitydetermining whether there are redundant labels and which of theseredundant labels should be discarded. Finally, as shown in FIG. 5B, themap data with the stitched paths (including its pared-down label data)is transmitted wirelessly to the device (step 634) which can thenefficiently render the stitched paths and associated labels.

Regardless whether client-side stitching (FIG. 5A) or the more efficientserver-side pre-stitching (FIG. 5B) is performed, the rendering oflabels can further include a step (not shown in these flowcharts) ofverifying that the labels do not interfere with other labels. Forexample, this step of verifying that the labels do not interfere withother labels may involve a step of generating a collision-avoidancearray representative of the map to be rendered for provisionally testingpotential map positions prior to actually rendering the map. This“virtual rendering” enables the map application to ascertain that labelsdo not collide (conflict) or overlap with other labels for which a mapposition has been previously assigned.

For the purposes of this specification, “label” includes not only allconventional forms of labels, such as city names, street names, etc, butalso any symbols or icons, such as highway number icons, or symbols oricons used to denote airports, tourist information kiosks, campgrounds,ferry crossings, etc. on large scale (regional) maps or restaurants,hotels, bus stations, etc. on city maps.

For the purposes of this specification, a “path” includes a road,street, highway, bicycle path, walkway or other route and also includeswaterway features such as a river, lake, bay, strait or any body ofwater for which three or more segments or constituent elements mayconverge, each having the same label as a result of being obtained fromseparate sets of map data for which individual labels are provided.

FIG. 6 schematically depicts the process of reconstructing (“stitching”)paths and/or map features either server-side or client-side in order toefficiently generate aesthetically-labelled maps for being displayed onwireless communications devices. By way of overview, for client-sidestitching, map data (which includes label data) is obtained by thewireless device from a map server in the form of Data Entries (“DEntries”). Alternatively, for server-side pre-stitching, the map data isprovided to a server having a pre-stitching module for performing thesteps of this technique server-side. Different layers of these D Entriesare used to render features of the same type or class. Thus, forexample, one layer of D Entries may be for lakes, rivers and bodies ofwater, while another layer of D Entries may be for highways, roads andstreets. This layered implementation enables context-filtering ofdesired or pertinent map data so that only desired or pertinent featuresare rendered onscreen.

In the example depicted in FIG. 6, the map is rendered from threeseparate D Entries (or three separate groups of D Entries from differentlayers). For the sake of illustration, the three D Entries (D Entry #1,D Entry #2, and D Entry #3) are rendered together to reconstitute acomposite path. As each D Entry has its own (independent) path label,simply rendering the map data as a composite map would unacceptablyresult in redundant labelling. Thus, to avoid rendering three pathlabels (two of which would be redundant), the server pre-stitches thepath segments (or alternatively) the map application on the clientdevice performs the “stitching” of path segments in order to reconstructthe path, i.e. a reverse segmentation.

However, a problem arises when attempting to aesthetically label aY-intersection, as was mentioned at the outset. For example, in aY-intersection map 700 shown in FIG. 6, the path has three segmentsbeing reassembled from discrete sets of map data. These are (i) a firstpath segment (upper branch 702) of the bifurcated/split path; (ii) asecond path segment (lower branch 704) of the bifurcated/split path; and(iii) a third path segment which is the “tail” or “stem” representingthe merged portion 706 of the path.

As each of the three path segments has its own label, which happens tobe identical to the others (because each segment actually represents apart of the same path), it is necessary to stitch the path back togetheragain to eliminate redundant labels. However, this stitching should bedone to avoid wrapping or folding the label back onto itself, as shownin FIG. 6. This “fold-back” problem occurs when the stitching algorithmin the map application stitches the first segment (upper branch 702) tothe second segment (lower branch 704). This conventional stitchingtechnique is based on a first-in-first-out (FIFO) approach, a.k.a.first-come first-served, meaning that a list of segments and theirlabels is compiled and searched, and the first two segments having thesame label and a common endpoint are stitched together without lookingbeyond the first two segments to see whether there is a third segmenthaving the same label and common endpoint). This FIFO-based stitchingcan result in a reconstructed path (the first path segment+the secondpath segment) with the third path segment remaining as its own“unstitched” segment. However, when the map application attempts torender the label at the center of the reconstructed path, the label endsup being placed where the angle is smallest and thus where the labelappears worst (because it ends up being wrapped/folded back onto itselfin a undesirable manner, as shown in FIG. 6). The unstitched segment ispreferably not labelled but in some cases it can be labelled in additionto the labelling of the reconstructed path. In another implementation, acollision-avoidance algorithm can be used to determine which of the twolabels should be rendered, i.e. the label for the reconstructed path orthe label for the unstitched path. Alternatively, another techniquewould entail rendering only one label along the longest path in thefield of view.

A solution to this problem is provided by the present technology. Theangles between each adjacent pair of path segments are determined andthe path segments subtending the largest angle are selected forstitching together (reconstruction). This results in the straightestpath being reconstructed along which the label can be rendered mostaesthetically. FIG. 7 schematically depicts this method of aestheticallylabelling a Y-intersection by stitching together the pair of adjacentpath segments subtending the largest angle. The result is that the firstpath segment 702 and the third path segment 706 are stitched together,leaving the second path segment 704 on its own (un-stitched to theothers). The label (e.g. “Path Label”) is then rendered centrally andaesthetically along the reconstructed path formed by stitching togetherthe first and third segments 702, 706. Stitching path segments createlonger (reconstructed) paths along which it is easier to render a labelwithout colliding with other labels. When this is done server-side,redundant labels can be eliminated to minimize the label data that mustbe transmitted wirelessly to the wireless handheld device.

FIG. 8 schematically depicts an angle determination based on vector pathsegments for the segments forming the Y-intersection. In order words,since the path segments are in vector format, one very efficient way ofcomputing the angles between adjacent pairs of segments is to computethe angles between vector path segments 1, 2 and 3, as shown in FIG. 8.The numerical values of the angles are presented merely by way ofillustration. As will be readily appreciated, once two of the threeangles are computed, the third can be readily deduced from the principlethat the sum of the three angles must equal 360 degrees. Alternatively,all three angles can be computed directly from the vectors and then theangles can be double-checked by ensuring that their sum equals 360degrees.

As shown in the example presented in FIG. 8, it may occur that there isno one largest angle because two of the angles are equal. To cope withthis possibility, the map application on the client device (or thepre-stitching server in the case of the server-side implementation)could optionally include a “tiebreaker” algorithm for determining whichof the two pairs of path segments is to be stitched. For example, themap application (or pre-stitching server) could consider proximity toother labels (for optimal readability) or alternatively the mapapplication (or server) could stitch the pair of segments that producesthe most horizontally level label. If none of these tiebreakers yield awinner, as a further tiebreaker, the map application (or server) couldarbitrarily select the two path segments that results in the label beingrendered along the top branch of the split. Ultimately, if there is noother basis to choose one or the other of the two pairs of pathsegments, the map application (or server) could randomly select one orthe other.

Once the label is rendered (or at least provisionally rendered ifcollisions or conflicts with other labels are to be checked prior toactually rendering onscreen), then there is generally no point inrendering the label along the third segment, which has remained as anindependent segment un-stitched to the reconstructed path. In otherwords, once the map application (or pre-stitching server) renders (orprovisionally renders) a label along a reconstructed path, any furtheror subsequent labels to be rendered are preferably discarded (i.e. notrendered) if they are identical to any previously rendered (orprovisionally rendered) labels. However, another technique would be tofeed both labels, i.e. the label associated with the reconstructed pathand the label associated with the unstitched path into acollision-avoidance algorithm to determine which is more suitablevis-à-vis other labels of higher or equal priority. Alternatively, thechoice can be made on the basis of which of the two labels is mosthorizontally level and/or which of the reconstructed path and unstitchedpath segment is longest in the field of view (which is usually, but notnecessarily, the reconstructed path).

FIG. 9 schematically depicts another example involving labelling of acul-de-sac formed from three (asymmetrical) path segments, i.e. a firstpath segment 702 obtained from D Entry #1, a second path segment 704obtained from D Entry #2, and a third path segment 706 obtained from DEntry #3. The vector angle analysis is depicted in FIG. 10. Vectordirections, taken at the point of convergence 710, are used to calculatethe angles between each adjacent pair of path segments. Vector pathsegment 1 and vector path segment 3 subtend the largest angle (in thisexample, 168 degrees), and therefore these path segments are stitchedtogether to provide the straightest-available reconstructed path alongwhich the label can be aesthetically rendered. FIG. 10 shows the vectorangle determination for the example of FIG. 9. Again, the vectordirections are taken at the point of convergence in this example.Another technique would entail determining an average vector directionover a predetermined range, rather than looking only the vectordirection at the point of convergence. In other words, thisslope-averaging technique would sample the slope of the path segment ata number of points starting from the point of convergence and compareaverage slope (direction) with the averages obtained for the adjacentsegments in order to arrive at an average angle.

FIG. 11 schematically depicts yet another example involving labelling ofa waterway having three path segments. In this example, it should bereadily appreciated, as was mentioned earlier, that “path” is to beconstrued expansively to include waterways, such as the river shown inFIG. 11, where three constituent segments (each downloaded as a separateD Entry) converge in a manner that is analogous to a Y-intersection on aroad.

In the example presented in FIG. 11, the upper and lower branches of theriver (i.e. the first segment 702 and the second segment 704) split fromthe merged portion (third segment 706), such as, for example, when theriver bifurcates around an island, in which case the same label is to beused to label the north channel (first segment) and the south channel(second segment), not to mention the merged portion 706. As was done forthe Y-intersection in FIG. 7 and the cul-de-sac in FIG. 9, the label isrendered (preferably centrally) along the reconstructed path formed bystitching together the two path segments that subtend the greatestangle. In this case, as demonstrated in FIG. 12, a vector angledetermination for FIG. 11 establishes that the pair of path segmentssubtending the greatest angle is composed of the first path segment 702and the third path segment 706.

The stitching in this example is preferably done server-side, although,as noted above, it can also be done client-side (i.e. directly on thedevice based on “raw” map data). Server-side pre-stitching ispreferable, however, because this eliminates label redundancy at theserver, thus reducing the amount of label data transmitted to thewireless device. Furthermore, the real-time angle calculations needed torender the labels on the map are computationally intensive, thusburdening the onboard processor on the client device.

Irrespective of whether stitching is performed server-side orclient-side, the stitching (reconstruction) of path segments provideslonger paths along which labels can be aesthetically placed and providesleeway to displace labels where they interfere with other labels ofhigher or equal priority. Once path segments are stitched, the label ispreferably placed centrally vis-à-vis the path (and/or optionallyrelative to other path/feature characteristics such as size, thickness,or rendering attributes). The decision whether to render a label alongboth the reconstructed path and the unstitched path (or only one or theother) can be (optionally) determined using a collision-avoidancealgorithm or with regard to which path is longest in the current fieldof view.

The foregoing method steps can be implemented as coded instructions in acomputer program product. In other words, the computer program productis a computer-readable medium upon which software code is recorded toperform the foregoing steps when the computer program product is loadedinto memory and executed on the microprocessor of the wirelesscommunications device.

This new technology has been described in terms of specificimplementations and configurations which are intended to be exemplaryonly. The scope of the exclusive right sought by the Applicant istherefore intended to be limited solely by the appended claims.

1. A method of stitching multiple converging paths of a map to bedisplayed on a wireless communications device, the method comprisingsteps of: providing map data for rendering the map on a display of thedevice, the map data including label data for labelling paths on themap; identifying at least three path segments that converge to a commonpoint on the map, each of the path segments having an identical label;determining an angle subtended by each pair of adjacent path segments inorder to identify which pair of adjacent path segments subtends thelargest angle; and generating a reconstructed path by stitching togetherthe pair of adjacent path segments subtending the largest angle.
 2. Themethod as claimed in claim 1 further comprising a step of rendering asingle instance of the label along the reconstructed path.
 3. The methodas claimed in claim 1 wherein the steps of identifying, determining andgenerating are performed on a server.
 4. The method as claimed in claim1 wherein the steps of identifying, determining and generating areperformed on a wireless communications device.
 5. The method as claimedin claim 1 wherein the step of determining the angle subtended by eachpair of adjacent path segments comprises steps of: determining vectordirections for each of the path segments at the common point where thepath segments converge; and computing angles between adjacent vectors.6. The method as claimed in claim 1 wherein the step of rendering asingle instance of the label comprises steps of: determining a center ofthe reconstructed path; and verifying whether placement of the label atthe center of the reconstructed path interferes with any other label. 7.The method as claimed in claim 1 wherein the step of identifying atleast three path segments that converge to a common point on the mapcomprises a step of identifying a Y-intersection having exactly threepath segments.
 8. The method as claimed in claim 1 wherein the step ofdetermining an angle in order to identify which pair of adjacent pathsegments subtends the largest angle comprises a further step ofdetermining, in a case where two of the largest angles are equal, whichof the adjacent path segments would result in a more horizontally levellabel.
 9. A computer program product comprising a computer-readablemedium having code executable by a processor to perform the steps of:providing map data for rendering the map on a display of the device, themap data including label data for labelling paths on the map;identifying at least three path segments that converge to a common pointon the map, each of the path segments having an identical label;determining an angle subtended by each pair of adjacent path segments inorder to identify which pair of adjacent path segments subtends thelargest angle; and generating a reconstructed path by stitching togetherthe pair of adjacent path segments subtending the largest angle.
 10. Thecomputer program product as claimed in claim 9 wherein thecomputer-readable medium further comprises code to perform a step ofrendering a single instance of the label along the reconstructed path.11. The method as claimed in claim 9 wherein the steps of identifying,determining and generating are performed on a server.
 12. The method asclaimed in claim 9 wherein the steps of identifying, determining andgenerating are performed on a wireless communications device.
 13. Thecomputer program product as claimed in claim 9 wherein the step ofdetermining the angle subtended by each pair of adjacent path segmentscomprises steps of: determining vector directions for each of the pathsegments at the common point where the path segments converge; andcomputing angles between adjacent vectors.
 14. The computer programproduct as claimed in claim 9 wherein the step of rendering a singleinstance of the label comprises steps of: determining a center of thereconstructed path; and verifying whether placement of the label at thecenter of the reconstructed path interferes with any other label. 15.The computer program product as claimed in claim 9 wherein the step ofidentifying at least three path segments that converge to a common pointon the map comprises a step of identifying a Y-intersection havingexactly three path segments.
 16. The computer program product as claimedin claim 9 wherein the step of determining an angle in order to identifywhich pair of adjacent path segments subtends the largest anglecomprises a further step of determining, in a case where two of thelargest angles are equal, which of the adjacent path segments wouldresult in a more horizontally level label.
 17. A wireless communicationsdevice for enabling a user of the device to display a map on the device,the wireless device comprising: an input device for enabling the user tocause the device to obtain map data for rendering the map to bedisplayed on a display of the device, the map data including label datafor labelling paths on the map; and a memory for storing code toinstruct a processor to: identify at least three path segments thatconverge to a common point on the map, each of the path segments havingan identical label; determine an angle subtended by each pair ofadjacent path segments in order to identify which pair of adjacent pathsegments subtends the largest angle; generate a reconstructed path bystitching together the pair of adjacent path segments subtending thelargest angle; and render a single instance of the label along thereconstructed path.
 18. The wireless communications device as claimed inclaim 17 wherein the processor determines the angle subtended by eachpair of adjacent path segments by: determining vector directions foreach of the path segments at the common point where the path segmentsconverge; and computing angles between adjacent vectors.
 19. Thewireless communications device as claimed in claim 17 wherein theprocessor renders a single instance of the label comprises by:determining a center of the reconstructed path; and verifying whetherplacement of the label at the center of the reconstructed pathinterferes with any other label.
 20. The wireless communications deviceas claimed in claim 17 wherein the processor identifies at least threepath segments that converge to a common point on the map by identifyinga Y-intersection having exactly three path segments.
 21. The wirelesscommunications device as claimed in claim 17 wherein the processorfurther determines, in a case where two of the largest angles are equal,which of the adjacent path segments would result in a more horizontallylevel label.